1. Field of the Invention
The present invention relates to a method for stabilizing bitumen-polymer blends and to novel plastic bituminous compositions produced thereby which are especially useful in roofing, paving and adhesives applications. The invention also relates to articles having self-adhesive properties based on such plastic bituminous compositions. The compositions according to the present invention comprise at least a bituminous component, a thermoplastic polymeric component and an ethylene-propylene-styrene block copolymer.
2. Prior Art
Since the late 1960's, styrene-butadiene rubber and styrene-rubber block copolymers have been used to dramatically improve the thermal and mechanical properties of asphalts. Practical application of the rubber addition approach requires that the blended product retain improved properties and homogenity during transportation, storage, and processing. Long term performance of elastomer-modified asphalts also depends on the ability of the blend to maintain thermal and chemical stability.
In the past, it was discovered that selection of a particular bitumen played an important role in the long term thermal, mechanical and chemical stability of the blended product. This lead to much research on the compatibility of thermoplastic polymers with various types of asphalts. Results of this research stressed a need for the use of "special" bitumen's to develop premium quality products with improved and/or stabilized properties. It was determined that in part, the reduction in material properties observed for "incompatible" bitumens resulted from the advancement of microphase separation. Previous attempts have been made to stabilize the thermal, mechanical, and chemical properties of incompatible thermoplastic rubber-asphalt blends. Those attemps have been based on the chemical modification of the asphalt. The microphase separation occurs between the asphaltene and maltene rich phases of elastomer modified blends.